June 15, 2017

Abstract: Blumeria graminis f. sp. hordei (Bgh) is the causal agent of powdery mildew on barley. Bgh secretes over 700 proteins that may function to modify host processes for colonization. Differential expression analysis of Bgh genes encoding secreted proteins in an isogenic panel of host immune signaling mutants, including a novel mutation Rar3 (Required for Mla6 Resistance3), identified fungal membrane trafficking genes. Infection phenotyping and kinetics show that immune compromised mutants have similar fungal growth, thereby, attributing any differences observed in expression to mutation rather than development. Thus, we hypothesize that powdery mildew genes may be targeting the host membrane trafficking pathway to both internalize effector proteins and suppress plant defense signal relay. Next, to address the modulation of host membrane trafficking genes, we utilized differential expression analysis. This identified # genes in all immune-compromised mutants, including ADP Ribosylation Factor 1 (ARF1) during host penetration by Bgh. ARF1 is a GTP-binding protein, involved in protein trafficking, ER-to-Golgi transport and Golgi-derived transport to the plasma membrane. Further, we show that ARF1 is a candidate interactor for MLA6, and a negative regulator cell death. Additionally, we utilized an expression Quantitative Trait Locus (eQTL) approach to focus on genes associated with Mla. This led to the discovery of 3,296 genes, including those in membrane trafficking pathways, that are directly or indirectly regulated by the Mla region (1HS). Taken together, these results corroborate the pivotal role membrane trafficking plays in R gene-mediated defense against powdery mildew.